I drive a 2001 Toyota Sienna. I carry my firearm at the 4:00 position, which makes it VERY easy to get to and doesn't get tangled up in my seat belt (which fastens at roughly the 3:00 position). I can access my firearm while sitting upright and buckled in; mounting it under the dash requires leaning forward to reach it - which takes precious time to grab, orient and shoot.
"...I advise the gun. While this gives a moderate exercise to the body, it gives boldness, enterprize, and independance to the mind... Let your gun therefore be the constant companion of your walks," Thomas Jefferson